1. Field of the Invention
This invention relates generally to mechanical joint restraint devices and more particularly to a thrust force restraining device for connecting pipes via mechanical joints.
2. Description of the Related Art
Mechanical joints of various configurations, such as T-joints, bends, lateral joints, cross joints, etc., are commonly utilized in connecting pipes for transporting fluids therethrough. Mechanical junction holders (mechanical restraint devices) of various types have been used to connect pipes to mechanical joints and to restrain such pipes against thrust forces present when fluids flow through the pipes. One such pipe junction holder is disclosed in U.S. Pat. No. 4,092,036. FIGS. 1a-b show the components of such a device and FIG. 1c shows a cross-section of a pipe 10 connected to a mating end 31 of a mechanical joint 30 by the device shown in FIGS. 1a-b. The mating end 31 of commonly used mechanical joints, such as the mechanical joint 30 shown in FIG. 1c contains a flange 32 extending outward of the body 33 having a socket end (conical open end) 34 whose interior surface 34a has a progressively increasing diameter that terminates near the end of the flange face 35. The flange 32 has a plurality of through holes 36 along its outer periphery in which bolts may be placed for attaching the flange 32 with other devices.
To sealingly connect the pipe 10 with the mechanical joint 30, a gasket 38 (FIG. 1a) having an outer surface 38a that substantially conforms to the interior surface 34a of the mouth 34 is seated in the socket end 34. A gland 40 (FIG. 1b) having a plurality of holes 41 along its outer periphery that match in location with the holes 36 of the mechanical joint 30 is placed around the pipe 10. Bolts, such as bolt 42, are placed through the holes 36 and 41 to secure the gasket 38 in the mouth 34. As the bolts 42 are tightened, the edge 44 of the gland 40 urges the gasket 38 against the mouth 34 to provide a seal between the pipe 10 and the mechanical joint 30. The gland 40 also contains a plurality of integral spaced clamping blocks 45, each such clamping block including a lateral top wall 45a which extends sloped downward and away from the edge 44. A through-hole 48 is provided in the lateral top wall 45a for inserting therethrough a bolt 49, which causes the teeth 51 of a clamping member 50 attached thereto to bite into the pipe 10 when the bolt is tightened, thereby restraining the pipe in position.
Such a pipe junction holder is not suitable for use with commonly used non-metallic pipes, such as Poly Vinyl Chloride ("PVC") pipes, because the clamping member 50 damages the pipe 10. Additionally, such an arrangement does not restrain the pipe 10 substantially along the entire periphery, i.e., 360.degree., of the pipe 10, which is highly desirable because such systems generally provide better clamping action.
Another prior art clamping device is shown in FIGS. 2a-d. It includes a gasket 38 (FIG. 1a), a ring wedge 60 having teeth 62 along its interior diameter and a gland 65 having a plurality of through holes 68 along its outer periphery that match in location with the holes 36 in the mechanical joint 30 (FIG. 2d). The outer surface 63 of the wedge 60 has a reducing slope. The inner surface 67 of the gland 65 is sloped so that it slides over the wedge's outer surface 63. The wedge 60 has a small opening 61 along its entire axial direction so that when the gland 65 is forced to slide over the ring wedge 60, it causes the wedge's inner diameter to decrease. To connect the pipe 10 with the mechanical joint 30, the gasket 38 is first seated or placed in the socket end 34 of the mechanical joint 30. The wedge 60 is then placed juxtaposed to the gasket 38 so that its outer surface 63 slopes downward away from the mechanical joint 30. The gland 65 is then slid over the gasket 38 and secured to the mechanical joint 30 by bolts 42 placed in the holes 36 of the coupling 31 and the corresponding holes 68 of the gland 65. The tightening of the bolts 42 causes the gland 65 to slide over the wedge 60, which causes the inner diameter of the wedge 60 to reduce in size and thereby urges the teeth 62 to bite into the pipe 10, which holds the pipe in place.
A disadvantage of such a device is that it frequently does not provide a proper seal between the pipe 10 and the mechanical joint 30. This is because the wedge 60 does not always exert adequate axial force "F" to cause the gasket 38 to attain a proper seal between the pipe 10 and the mechanical joint 30. Frequently, as the bolts 42 are tightened, the wedge 60 engages with the pipe 10 before the seal is accomplished by the gasket 38. To correct this problems, the pipe fitters either apply greater than the recommended torque to the bolts 42, which can damage the pipes, or by repeating the clamping procedure, which incurs undesired delays and expense.
The present invention addresses the above-noted problems and provides a universal mechanical junction holder for sealingly coupling metallic and non-metallic pipes with mechanical joints. The system also preferably utilizes the bolt described in the U.S. patent application Ser. No. 08/491,270, which is incorporated herein by reference, to ensure that the torque applied to the clamping member does not exceed a predetermined amount.